1. Field of the Invention
The present invention relates to spin-valve thin-film elements in which the resistivity is varied by the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by an external magnetic field. In particular, the present invention relates to a magnetoresistive element which can effectively conduct a detecting current to a multilayered film included therein and a method for making the magnetoresistive element.
2. Description of the Related Art
FIG. 21 is a cross-sectional view at an air bearing surface (ABS) of a conventional magnetoresistive element. This magnetoresistive element is called a spin-valve thin-film element which is one of giant magnetoresistive (GMR) elements using a giant magnetoresistive effect, and detects a recorded magnetic field from magnetic media such as a hard disk.
The spin-valve thin-film element has a multilayered film 10 composed of, from the bottom, a second antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic conductive layer 3, and a free magnetic layer 4. The second antiferromagnetic layer 1 is generally composed of an iron-manganese (Fexe2x80x94Mn) alloy or a nickel-manganese (Nixe2x80x94Mn) alloy. Each of the pinned magnetic layer 2 and the free magnetic layer 4 is generally composed of a nickel-iron (Nixe2x80x94Fe) alloy. The nonmagnetic conductive layer 3 is generally composed of copper (Cu).
As shown in FIG. 21, the thickness of the free magnetic layer 4 is smaller in both side regions A in the track width direction (X direction in the drawing) than that in the central region B. Ferromagnetic layers 5 formed of, for example, a Nixe2x80x94Fe alloy are provided on the side regions A.
A pair of first antiferromagnetic layers 6 is formed on the ferromagnetic layers 5 and is separated at an interval of the track width Tw. In conventional technology, the first antiferromagnetic layers 6 are composed of an iridium-manganese (Irxe2x80x94Mn) alloy or the like. Moreover, conductive layers 7 formed of chromium (Cr) are provided on the first antiferromagnetic layers 6.
In this spin-valve thin-film element, a lower gap layer 8 is provided under the second antiferromagnetic layer 1, and an upper gap layer 9 is provided over the conductive layers 7. The lower gap layer 8 and the upper gap layer 9 are composed of an insulating material such as alumina (Al2O3).
The magnetization of the pinned magnetic layer 2 is aligned in a single-domain state in the Y direction (the direction of the fringing magnetic field from the recording medium, that is, the height direction) by exchange anisotropic magnetic field between the pinned magnetic layer 2 and the second antiferromagnetic layer 1. Exchange anisotropic magnetic fields are generated between the ferromagnetic layers 5 and the first antiferromagnetic layers 6 and between the ferromagnetic layers 5 and the free magnetic layer 4 at the side regions A, and magnetize the ferromagnetic layers 5 and the free magnetic layer 4 at the side regions A in the X direction. As a result, the magnetization of the free magnetic layer 4 is affected by the bias magnetic field from the ferromagnetic layers 5 and the free magnetic layer 4 at the side regions A and is aligned in the X direction. Accordingly, the magnetization of the pinned magnetic layer 2 and the magnetization of the free magnetic layer 4 are orthogonal.
In this spin-valve thin-film element, a detecting current which is supplied from the conductive layers 7 via the first antiferromagnetic layers 6 flows in the pinned magnetic layer 2, the nonmagnetic conductive layer 3, and the free magnetic layer 4. The recording medium such as a hard disk moves in the Z direction, and a fringing magnetic field from the recording medium is oriented in the Y direction. This fringing magnetic field changes the magnetization direction of the free magnetic layer 4 from the X direction to the Y direction. The resistivity of the element is varied by the relationship between the variable magnetization direction of the free magnetic layer 4 and the pinned magnetization direction of the pinned magnetic layer 2. Such a change in resistivity is called a magnetoresistive effect and is detected as a change in voltage. The fringing magnetic field from the recording medium is detected in such a manner.
The magnetoresistive element shown in FIG. 21, however, has the following problems. Since the conductive layers 7 are formed on the first antiferromagnetic layers 6, the detecting current flows in the pinned magnetic layer 2, the nonmagnetic conductive layer 3, and the free magnetic layer 4, via the first antiferromagnetic layers 6. Since the first antiferromagnetic layers 6 are formed of an antiferromagnetic material such as an Irxe2x80x94Mn alloy having relatively large resistivity, the detecting current flowing in the multilayered film 10 is reduced.
As described above, the magnetization of the free magnetic layer 4 is oriented in the X direction by the bias magnetic field due to the exchange anisotropic magnetic field which is generated between the ferromagnetic layers 5 and the first antiferromagnetic layers 6. The free magnetic layer 4 is firmly magnetized in the X direction at boundary regions D near the ferromagnetic layers 5 by the effect of the strong bias magnetic field. Thus, the magnetization of the free magnetic layer 4 is not adequately varied by the external magnetic field.
The boundary regions D, which do not exhibit an adequate change in the magnetization, is called dead regions. Thus, the substantial sensitive region, which exhibits an adequate change in the magnetization by the effect of the external magnetic field and thus has a magnetoresistive effect, is a region of the track width Tw other than the dead regions. As a result, the dead regions significantly decrease the fraction of the detecting current in the sensitive region. Thus, a desired amount of detecting current does not flow in the sensitive region, resulting in the generation of noise and a decrease in read output.
Accordingly, it is an object of the present invention to provide a magnetoresistive element which can effectively conducts a detecting current to a triplelayered film including a free magnetic layer, a nonmagnetic conductive layer, and a pinned magnetic layer and having a magnetoresistive effect and which exhibits improved output characteristics.
It is another object of the present invention to provide a method for making the magnetoresistive element.
According to an aspect of the present invention, a magnetoresistive element comprises a multilayered film comprising a magnetic detecting layer having a magnetoresistive effect, a pair of first antiferromagnetic layers in contact with the magnetic detecting layer of the multilayered film at a predetermined gap in the track width direction, the first antiferromagnetic layers aligning the magnetization direction of the magnetic detecting layer, and a pair of conductive layers in contact with the pair of first antiferromagnetic layers, the pair of conductive layers applying a detecting current to the multilayered film. The first antiferromagnetic layers comprise an antiferromagnetic material having higher resistivity than that of the conductive layers, the conductive layers are superimposed with the corresponding first antiferromagnetic layers and are in contact with the magnetic detecting layer in a range of the predetermined gap, and the distance between the pair of conductive layers defines a track width when the multilayered film detects an external magnetic field.
As described above, the magnetoresistive element of the present invention has the pair of first antiferromagnetic layers in order to align the magnetization direction of the magnetic detecting layer of the multilayered film. The present invention is characterized in that the first antiferromagnetic layers comprise an antiferromagnetic material having higher resistivity than that of the conductive layers and that the conductive layers are superimposed with the corresponding first antiferromagnetic layers and are in contact with the magnetic detecting layer in a range of the predetermined gap.
Since the pair of conductive layers extend over the magnetic layer, the detecting current from the conductive layers effectively flows in the multilayered film without shunts in the first antiferromagnetic layers. Since the first antiferromagnetic layers are composed of the antiferromagnetic material having higher resistivity than that of the conductive layers, the shunts of the detecting current in the first antiferromagnetic layers can be effectively decreased. Moreover, the detecting current does not substantially flow in the dead regions not having the magnetoresistive effect and can effectively flows in a sensitive region having the magnetoresistive effect. As a result, output characteristics are improved compared to conventional magnetoresistive elements.
Preferably, the magnetoresistive element further comprises an insulating layer provided between the pair of conductive layers, each of the side faces of the insulating layer abutting each of the end faces of the conductive layers. The detecting current more adequately flows in the multilayered film.
Preferably, the multilayered film comprises a pinned magnetic layer having a pinned magnetization direction, a nonmagnetic conductive layer, and a free magnetic layer as the magnetic detecting layer having a variable magnetization direction with respect to an external magnetic field, the pair of first antiferromagnetic layers are in contact with the free magnetic layer at the predetermined gap in the track width direction, and the magnetization direction of the free magnetic layer is oriented in a direction which is perpendicular to the magnetization direction of the pinned magnetic layer by exchange anisotropic coupling with the first antiferromagnetic layers.
Preferably, the magnetoresistive element further comprises a pair of ferromagnetic layers provided on both sides of the magnetic detecting layer of the multilayered film, and the ferromagnetic layers are in contact with the corresponding first antiferromagnetic layers.
Preferably, the multilayered film comprises a pinned magnetic layer having a pinned magnetization direction, a nonmagnetic conductive layer, and a free magnetic layer as the magnetic detecting layer having a variable magnetization direction with respect to an external magnetic field, the first antiferromagnetic layers are in contact with the corresponding ferromagnetic layers lying at both sides of the free magnetic layer, and the magnetization direction of the free magnetic layer is oriented in a direction which is perpendicular to the magnetization direction of the pinned magnetic layer by exchange anisotropic coupling with the first antiferromagnetic layers. This magnetoresistive element is referred to as a spin-valve thin-film element.
Preferably in this case, both side regions of the free magnetic layer in the track width direction are thinner than the central region, the ferromagnetic layers are formed on the side regions, and the conductive layers extend over the free magnetic layer. Alternatively, the multilayered film may comprise a second antiferromagnetic layer, the magnetization direction of the pinned magnetic layer is pinned by exchange coupling with the second antiferromagnetic layer, the second antiferromagnetic layer extends in the track width direction than the pinned magnetic layer, the upper faces of the ferromagnetic layers are equal to or higher than the upper face of the free magnetic layer, the ferromagnetic layers are in contact with the corresponding first antiferromagnetic layers, and the first antiferromagnetic layers extend to a position in contact with the free magnetic layer.
Preferably, the first antiferromagnetic layers comprise an antiferromagnetic material having a blocking temperature which is lower than that of the second antiferromagnetic layer. The magnetization of the free magnetic layer is adequately oriented in a direction orthogonal to the magnetization of the pinned magnetic layer.
Preferably, the first antiferromagnetic layers comprise an antiferromagnetic material of an electrically insulating oxide. This material suppresses shunts of the detecting current to the first antiferromagnetic layers. More preferably, the electrically insulating oxide is selected from NiO and xcex1-Fe2O3.
Alternatively, the first antiferromagnetic layers may comprise one of an Xxe2x80x94Mn alloy and an Xxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy wherein X is at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os and Xxe2x80x2 is at least one element selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Ir, Sn, Hf, Ta, W, Re, Au, Pb, and rare earth elements.
According to another aspect of the present invention, a method for making a magnetoresistive element comprising the steps of:
(a) forming a multilayered film on a substrate by depositing a second antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer, in that order;
(b) forming a lift-off resist layer having cutout sections thereunder on the free magnetic layer;
(c) forming first antiferromagnetic layers on the free magnetic layer;
(d) forming conductive layers on the first antiferromagnetic layers obliquely with respect to the magnetic layer so that the conductive layers extend in the cutout sections of the resist layer, the first antiferromagnetic layers having higher electrical resistivity than that of the conductive layers; and
(e) removing the resist layer on the multilayered film.
In this method, using the lift-off resist, the ferromagnetic layers and the first antiferromagnetic layers are formed on both side of the multilayered film, and the conductive layers are formed obliquely with respect to the multilayered film. This oblique process enables the formation of the conductive layers in the cutout sections of the resist layer. Thus, the resulting conductive layers extend on the free magnetic layer.
Preferably, an insulating layer is formed on the free magnetic layer in the step (a), the lift-off resist layer is formed on the insulating layer in the step (b), the method further comprises the step (f) of etching both side faces in the track width direction of the insulating layer to expose the surface of the free magnetic layer between the step (b) and the step (c), and each of end faces of the conductive layers is put into contact with each of the side faces of the insulating layer in the step (d).
In the step (c), ferromagnetic layers may be formed on both sides of at least the free magnetic layer. Thus, the first antiferromagnetic layers are formed on the corresponding ferromagnetic layers.
Preferably, in the step (c), the thickness of the free magnetic layer is reduced in both side regions in the track width direction, and the ferromagnetic layers are formed on the side regions.
Preferably, in the step (c), the both sides in the track width direction of the multilayered film are etched so that the second antiferromagnetic layer is exposed, and the ferromagnetic layers are formed on the second antiferromagnetic layer so that the upper faces of the ferromagnetic layers are equal to or higher than the upper face of the free magnetic layer.
Preferably, in the step (c), the substrate provided with the magnetic layer is placed vertically with respect to a target, and the first antiferromagnetic layers are formed by one of an ion-beam sputtering process, a long-throw sputtering process, and a collimation sputtering process, and, in the step (d), the substrate is tilted with respect to a target having a composition for the conductive layers or the target is tilted with respect to the substrate, and the ferromagnetic layers as the optional layers and the conductive layers are formed on the first antiferromagnetic layers and in the cutout sections of the lift-off resist by one of an ion-beam sputtering process, a long-throw sputtering process, and a collimation sputtering process.
Preferably, the first antiferromagnetic layers comprise an antiferromagnetic material having a blocking temperature which is lower than that of the second antiferromagnetic layer. The magnetization of the free magnetic layer is adequately oriented in a direction orthogonal to the magnetization of the pinned magnetic layer.
Preferably, the first antiferromagnetic layers comprise an antiferromagnetic material of an electrically insulating oxide. More preferably, the electrically insulating oxide is selected from NiO and xcex1-Fe2O3.
Alternatively, the first antiferromagnetic layers may comprise one of an Xxe2x80x94Mn alloy and an Xxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy wherein X is at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os and Xxe2x80x2 is at least one element selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Ir, Sn, Hf, Ta, W, Re, Au, Pb, and rare earth elements.